my pc says Firefox is running after I close the browser, and will not let me access the internet. This continues even after I shut down and restart my pc. It even continues to do it after I uninstal, then reinstal Firefox. What can I do?

We tried uninstalling, then reinstalling Firefox, but still get the same error message.

We also went into our Task Manager which told us Firefox was running. We told the TM to close it, which it said it did, but we still get the error, and cannot access the web.